Option 2: Password-protected archive file.
To send or receive an attachment that is being blocked, the sender of the message must first place the file into a password-protected archive file, then attach it to the message. There are a variety of Windows and Macintosh programs that can create these files, including WinZip and StuffIt.

The sender should include instructions in the email telling the recipient the archive type and contents and let the recipient know what the password is to the protected file.

Password-protected archives should NEVER be used to transmit any data that is confidential or protected, because password-protected archives are easy to decode by any determined hacker.

Is it possible to simply replace the file extension with an unblocked file extension?

Renaming the file extension won't work. The scanning software can detect the blocked filetypes, even when the file is renamed.

Why is my archive file being blocked?

Archive files are NOT automatically blocked. The only time an archive file is not delivered is when it contains a file that is of a blocked file type.

If an archive file is blocked, the sender needs to put the archive file into a password protected archive file (an archive within an archive), then send that file to the recipient.

The sender should include instructions in the email telling the recipient the archive type and contents. As the sender, let the recipient know what the password is to the protected file.

Password-protected archives should NEVER be used to transmit any data that is confidential or protected, because password-protected archives are easy to decode by any determined hacker.